UHCI: module parameter to ignore overcurrent changes

Certain boards seem to like to issue false overcurrent notifications,
for example on ports that don't have anything connected to them.  This
looks like a hardware error, at the level of noise to those ports'
overcurrent input signals (or non-debounced VBUS comparators).  This
surfaces to users as truly massive amounts of syslog spam from khubd
(which is appropriate for real hardware problems, except for the
volume from multiple ports).

Using this new "ignore_oc" flag helps such systems work more sanely,
by preventing such indications from getting to khubd (and spamming
syslog).  The downside is of course that true overcurrent errors will
be masked; they'll appear as spontaneous disconnects, without the
diagnostics that will let users troubleshoot issues like
short-circuited cables.  In addition, controllers with no devices
attached will be forced to poll for new devices rather than relying on
interrupts, since each overcurrent event would generate a new
interrupt.

This patch (as826) is essentially a copy of David Brownell's ignore_oc
patch for ehci-hcd, ported to uhci-hcd.

Signed-off-by: Alan Stern <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Documentation/kernel-parameters.txt

@@ -1714,6 +1714,14 @@ and is between 256 and 4096 characters. It is defined in the file
 	uart6850=	[HW,OSS]
 			Format: <io>,<irq>
 
+	uhci-hcd.ignore_oc=
+			[USB] Ignore overcurrent events (default N).
+			Some badly-designed motherboards generate lots of
+			bogus events, for ports that aren't wired to
+			anything.  Set this parameter to avoid log spamming.
+			Note that genuine overcurrent events won't be
+			reported either.
+
 	usbhid.mousepoll=
 			[USBHID] The interval which mice are to be polled at.